Where in Okinawa to you intend to go?
When I visited Naha, I had great izakaya food on Zamami Island. The best spot I found was Santa, 三楽, an izakaya near the port. Zamami Island's guide has information here. I had classic Okinawan dishes such as rafute, goya chamburu, and mozuku. The master there is friendly and welcomes parties. I got talking to other guests there, too. It's a friendly, casual, and big comfortable space.
Okinawa has been maintaining its own unique food culture for a long time.
I recommend you to try one of the must-eat Okinawa cuisines is Okinawa soba, a.k.a Sōki soba. Among other Okinawa soba specialty shops, one of the most popular and renowned places is Ryukyu Soba Ashibiuna (琉球茶房あしびうなぁ).
The building of Ashibiuna is a renovated version of an Okinawa traditional house built in the postwar era on the site of a royal family house of Ryukyu Kingdom. Shisa (‘Okinawa mythological creature and cultural artifact’) residing on the Okinawa traditional red roof tiles awaits to give you a warm welcome. From the seats on the terrace, you will enjoy the magnificent view of the well-kept stone garden. Ashibiuna provides not only Okinawa local cuisines, but also a cozy atmosphere of good old Okinawa.
For newcomers to Okinawa food culture, Ashibiuna would be the best option as a starter.
Price Range: 1,000~1,500 yen during lunch time/2,000~5,000 yen during dinner time.
Here is their official website. You can visit this http://www.ryoji-family.co.jp/ryukyusabo.html